Vented, gas-fired air heater

ABSTRACT

A vented, gas-fired air heater especially designed for temporary heating applications includes an improved burner design providing effective air and gas mixing and efficient burning in the combustion chamber. Highly efficient heat exchanger including corrugated heat exchanger panels provides enhanced heat transfer characteristics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/639,440, filed Dec. 14, 2006, which claims priority to CanadianPatent Application No. 2530544, filed Dec. 16, 2005, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is directed toward improvements in indirect fired,vented air heaters.

There are generally two categories of gas-fired heaters, direct-firedand indirect-fired (or vented) heaters. With a direct-fired heater, theproducts of combustion are released into the heated space. With anindirect-fired heater, some form of heater exchanger is used to transferthe heat from the combustion gases to the heated space. The combustiongases are vented out of the heated area.

Gas-fired heaters used in temporary heating applications, such as onconstruction sites, have generally been of the direct-fired type. Thereis currently an increasing demand for indirect-fired heaters for suchapplications. There is also an increasing demand for more energyefficient heaters. As a rule, heaters of higher efficiency are also muchlarger in size. The challenge is to have a relatively small yetefficient heater that can be used in temporary applications. Sincetemporary heaters are used seasonally, a smaller size would provide thebenefit of reduced costs for off-season storage.

SUMMARY OF THE INVENTION

The objects of this invention are to provide a heater that:

has a highly efficient heat exchanger with enhanced heat transfercharacteristics.

has an improved burner design providing a relatively short distancebetween the burner inlet and the flame.

provides a venturi action in the burner air flow at the burner head topromote air and gas mixing and efficient burning in the combustionchamber.

is economical to produce and operate.

is compact in size, with a relatively small footprint.

has a rugged construction that allows it to stand up to rigors both oftransportation between sites and of being used in applications such asconstruction sites.

A gas burner in accordance with one aspect of the invention includes anenclosure defining a path for movement of combustion air. A pair ofgenerally parallel burner plates are disposed transverse to the path ofcombustion air travel. The burner plates are spaced apart to define ashallow chamber therebetween and both plates have a plurality ofopenings therein allowing for passage of combustion air therethrough.The openings in a first one of said plates are aligned with respectiveones of the openings in the second plate to provide annular openingsallowing exit of gaseous fuel from the shallow chamber. A conduitsupplies gaseous fuel into the shallow chamber defined between saidburner plates such that, in use, combustion air moving along the pathand through the aligned openings in said burner plates mixes withgaseous fuel emerging from said chamber via said annular openingsthereby to provide a combustible fuel-air mixture downstream of saidburner plates.

The openings in said plates are preferably in the form of short tubularcollars projecting from said plates with the tubular collars of bothplates being aligned with and directed toward each other in confrontingspaced apart relation to provide said annular openings allowing exit ofgaseous fuel between the confronting spaced apart collars.

In another aspect of the invention, the first burner plate is locatedupstream of the second burner plate relative to the flow direction ofcombustion air when in use. The tubular collars of the first burnerplate define flow passages of smaller diameter than those defined by thetubular collars of the second plate thereby to create a venturi-likeflow action as the combustion air passes through the aligned tubularcollars thus promoting thorough mixing of the air and the gaseous fuelbeing supplied via said annular gaps as well as allowing for reduced gassupply pressure to the shallow chamber between the burner plates as theventuri action pulls the gas into the moving combustion air streams.This is the reverse of traditional venturi burners where higher gaspressures are used to draw combustion air in.

The short tubular collars are ideally integrally formed with theirrespective burner plates.

The burner plates are preferably of generally circular outline, withsaid conduit to supply gaseous fuel being connected centrally of saidplates to supply the fuel to the chamber defined between said plates.The conduit preferably has an end portion centrally disposed betweensaid burner plates and having a plurality of radially arranged openingsto assist in providing even distribution of gaseous fuel to saidchamber.

The blower preferably includes a vaned rotor mounted for rotation on anaxis generally centered with said burner plates and extending normalthereto. Air flow confining structures are shaped to direct the air flowfrom said rotor generally along said axis whereby to deliver a generallyeven and balanced flow toward the burner plates to promote even flowdistribution through said openings therein.

In accordance with another aspect of the invention there is provided aheat exchanger section comprising a pair of metal panels disposed inclose face-to-face relation to allow gases to flow therebetween from aninlet end to an outlet end in a travel direction. The panels each haveundulations or corrugations therein whereby gases flowing between saidpanels in the travel direction are forced to move in a turbulent fashionto enhance transfer of heat between said panels and the flowing gases.

In a preferred form of the invention said panels each have corrugationstherein angled relative to the travel direction and oppositely orientedwith respect to each other such that adjacent corrugations are in acriss-cross relation to each other whereby gases flowing between saidpanels are forced by the opposing corrugations to move in the form of aseries of repeating spirals from said inlet end to said outlet end toprovide enhanced heat transfer. The corrugations are preferably of agenerally V-shaped or zig-zag configuration when seen end-on and aredisposed at a relatively shallow acute angle relative to a line normalto the travel direction. In one preferred embodiment, said acute angleis approximately 9 degrees with said adjacent corrugations being at anangle of approximately 18 degrees relative to each other.

An air heater combination in accordance with a further aspect of theinvention comprises a main housing having an air inlet and an outlet forheated air and a combustion chamber located therein. A burner assemblyis connected to the combustion chamber to supply burning gases thereto.An exhaust stack is provided and a heat exchanger is connected to saidcombustion chamber and comprises a plurality of heat exchanger sectionshaving inlet ends connected to receive heated combustion gases from thecombustion chamber and outlet ends connected to said exhaust stack forexhausting combustion gases after passage through the heat exchangersections. The heat exchanger sections are spaced apart to allow thepassage of air therebetween to effect heating of same. A blower assemblymoves cool air into said main housing via said air inlet and causes theair to travel between the heat exchanger sections and thence outwardlyof said outlet for heated air.

The heat exchanger sections of the air heater each preferably comprisemetal panels having corrugations or undulations therein arranged tocause combustion gases moving therethrough to move in a turbulentfashion to enhance transfer of heat from the gases to the metal panelswhile also causing turbulence in the air being heated as it travelsbetween the heat exchanger sections and enhancing heat transfer from themetal panels to the air being heated.

In a typical embodiment, the heat exchanger sections are disposed, inuse, in vertically spaced horizontal planes to provide for said passageof air along spaced horizontal planes during heating thereof.

Each said heat exchanger section in a preferred form of the inventioncomprises a pair of metal panels disposed in close face-to-face relationto allow gases to flow therebetween from the inlet ends to the outletends in a travel direction. Said panels each have corrugations thereinangled relative to the travel direction and oppositely oriented withrespect to each other such that adjacent corrugations are in acriss-cross relation to each other whereby gases flowing between saidpanels are forced by the opposing corrugations to move in the form of aseries of repeating spirals from said inlet end to said outlet end toprovide enhanced heat transfer.

The combustion chamber is preferably arranged in the main housing suchthat cool air entering via said air inlet travels partly around thecombustion chamber exterior and receives heat therefrom prior to passingbetween said heat exchanger sections.

An air heater according to a further aspect of the invention comprises amain housing having an air inlet and an outlet for heated air, acombustion chamber located therein, a burner assembly connected to thecombustion chamber to supply burning gases thereto, an exhaust stack, aheat exchanger connected to said combustion chamber and comprising aplurality of heat exchanger sections having inlet ends connected toreceive heated combustion gases from the combustion chamber and outletends connected to said exhaust stack for exhausting combustion gasesafter passage through the heat exchanger sections. Said heat exchangersections are spaced apart to allow the passage of air therebetween toeffect heating of same. A blower assembly moves cool air into said mainhousing via said air inlet and causes the air to travel between the heatexchanger sections and thence outwardly of said outlet for heated air.Said burner assembly includes an enclosure connected to the combustionchamber and defines a path for movement of combustion air toward thecombustion chamber. A pair of generally parallel burner plates aredisposed transverse to the path of combustion air travel. Said burnerplates are spaced apart to define a shallow chamber therebetween andboth plates have a plurality of openings therein allowing for passage ofcombustion air therethrough. The openings in a first one of said platesare aligned with respective ones of the openings in the second plate toprovide annular openings allowing exit of gaseous fuel from the shallowchamber. A conduit supplies gaseous fuel into the shallow chamberdefined between said burner plates such that, in use, combustion airmoving along the path and through the aligned openings in said burnerplates mixes with gaseous fuel emerging from said chamber via saidannular openings thereby to provide a combustible fuel-air mixturedownstream of said burner plates, which mixture, in use, is ignited toprovide the supply of burning gases to said combustion chamber.

The air heater burner preferably is constructed such that said openingsin said plates are in the form of short tubular collars projecting fromsaid plates with the tubular collars of both plates being aligned withand directed toward each other in confronting spaced apart relation toprovide said annular openings allowing exit of gaseous fuel between theconfronting spaced apart collars.

The air heater burner is typically arranged with said first burner platelocated upstream of the second burner plate relative to the flowdirection of combustion air when in use, and wherein the tubular collarsof the first burner plate define flow passages of smaller diameter thanthose defined by the tubular collars of the second plate thereby tocreate a venturi-like flow action as the combustion air passes throughthe aligned tubular collars thus promoting thorough mixing of the airand the fuel being supplied via said annular gaps.

The air heater burner plates may be of generally circular outline, withsaid conduit to supply gaseous fuel being connected centrally of saidplates to supply the fuel to the chamber defined between said plates,said conduit having an end portion centrally disposed between saidburner plates and having a plurality of radially arranged openings toassist in providing even distribution of gaseous fuel to said chamber.

The air heater typically employs a burner blower communicating with saidenclosure to provide for movement of combustion air along said path oftravel toward said burner plates and combustion chamber. The burnerblower preferably includes a vaned rotor mounted for rotation on an axisgenerally centered with said burner plates and extending normal thereto,the burner enclosure having a portion shaped to direct the air flow fromsaid rotor generally along said axis whereby to deliver a generally evenand balanced flow toward the burner plates to promote even flowdistribution through said openings therein.

The air heater heat exchanger sections each preferably comprise metalpanels having corrugations or undulations therein arranged to causecombustion gases moving therethrough to move in a turbulent fashion toenhance transfer of heat from the gases to the metal panels. These heatexchanger sections are disposed in a typical embodiment in verticallyspaced horizontal planes to provide for said passage of air along spacedhorizontal planes during heating thereof. The metal panels preferablyhave corrugations therein angled relative to the travel direction andoppositely oriented with respect to each other such that adjacentcorrugations are in a criss-cross relation to each other whereby gasesflowing between said panels are forced by the opposing corrugations tomove in the form of a series of repeating spirals from said inlet end tosaid outlet end to provide enhanced transfer of heat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of the complete air heater takenin a vertical plane.

FIG. 2 is a section view taken along line 2-2 of FIG. 1 in a horizontalplane.

FIG. 3 is a section view of the burner assembly.

FIG. 4 is a partial section view of the burner assembly showing theburner plates and gas feed assembly.

FIG. 5 is a bottom plan view of the burner plate structure of FIG. 4.

FIG. 6 is a further section view of the burner head assembly showinggas/air flows.

FIG. 7 is a perspective view of the combustion chamber, heat exchangerand exhaust stack assembly looking slightly from below.

FIG. 8 is a perspective view similar to FIG. 7 but looking somewhattoward to the upper side.

FIG. 9 is a top plan view of a heat exchanger section.

FIG. 10 is a side elevation view of the heat exchanger section.

FIG. 11 is a top plan view of a heat exchanger panel.

FIG. 12 is a view of the heat exchanger panel seen edge-on showing thecorrugations therein.

FIG. 13 is a diagrammatic view of a narrow slice of the heat exchangersection taken longitudinally thereof illustrating the face-to-facerelationship of the metal panels and the corrugations therein.

FIG. 14 is a diagrammatic plan view of a heat exchanger sectionillustrating the panel corrugations therein and their criss-crossrelationship.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The indirect fired, vented air heater 20 includes a rectangular box-likemain heater housing 22 having a burner assembly 24 mounted on an upperportion thereof and with a vertically disposed combustion chamber 26disposed within the main housing. A heat exchanger 28 is connected tothe combustion chamber 26 and extends laterally outwardly therefrom. Thecombustion chamber is positioned vertically within the main housing 22with the burner assembly 24 positioned above and connected to thecombustion chamber with the lower end of the burner assembly projectinginto the upper end of the combustion chamber. The heat exchanger 28includes a series of vertically spaced formed sections 30 which will bedescribed hereafter. These sections 30 are connected in sealedrelationship to slot-like openings in the walls of the combustionchamber on one side and to slot-like openings which are provided in thewalls of a vertically arranged exhaust stack 32 located in spacedrelation to the combustion chamber. A blower assembly 34 in the form ofa pair of relatively large blower fans 36 is positioned to the side ofthe combustion chamber 26 which is opposite to the side where the heatexchanger 28 is positioned. The inlet end of the main heater housing 22is provided with a rectangular inlet opening 38 for fresh cool air whichis drawn inwardly by the blower fans 36, forced around the exterior ofthe combustion chamber and then caused to pass between the spaced apartheat exchanger sections 30, with the heated air then passing through asimilarly sized warm air exit opening 40 in the exit or outlet end ofthe heater housing 22.

It will be appreciated that the indirect fired heater being describedmay be made in a variety of shapes and sizes while still retaining thebasic innovative features to be described in detail hereafter. Forexample, one particular unit having a heating capacity of 1,500,000BTU/hr., and fueled by either natural gas or propane, had overall heaterhousing dimensions of approximately 114 inches long by 32.5 inches wideby 77.5 inches high with a weight of 1,875 lbs. The above-mentioned coolair and warm air inlet and outlet openings 38, 40 at opposing ends ofthe housing were each 24 inches high by 24 inches wide. The air flowprovided by the above-mentioned blowers 36 (without duct work and at 20°C.) was in the order of 7300 ft³ per minute. The air temperature rise(without duct work) was 95° C. (171° F.) while the stack temperaturerise was measured as 192° C. (345° F.). These figures are given merelyby way of example and will of course vary widely depending on the sizeand exact design of the unit selected.

The gas burner assembly 24 (FIG. 3) includes a burner blower 44positioned above the burner head 45. The burner blower 44 is providedwith suitable air flow confining structures 46 including flowstraightening vanes 48 and conical section 49 defining a path formovement of combustion air downwardly toward the burner head having apair of generally parallel burner head plates 50,52 and disposedtransverse to the path of combustion air travel. Burner plates 50, 52are provided with upper and lower support plates 51, 53 respectively, tostiffen the burner head assembly and prevent warping of same, etc. Itwill be seen that the vaned burner blower rotor 56 is mounted forrotation on an axis defined by its vertical drive shaft 58 and isgenerally centered with the above-mentioned burner plates 50, 52 andextending normal thereto. (The drive shaft motor is not shown). The airflow confining structures 46 and vanes 48 are shaped to direct the airflow from the rotor 56 generally along this vertical axis thereby todeliver a generally even and balanced flow toward the burner plates 50,52 to promote even flow distribution through the openings therein whichwill be hereafter described.

As best seen in FIGS. 3-6, the burner plates 50, 52 are of generallycircular outline shape and they are spaced apart to define a shallowchamber 60 between them (FIGS. 4 and 6). Both plates have a multiplicityof openings 62, 64 therein allowing for passage of combustion air fromthe burner blower 44 therethrough. The openings 62 in a first one of theplates 50 are aligned with respective ones of the openings 64 in thesecond plate 52 to provide annular openings 66 allowing exit of gaseousfuel from the shallow chamber 60 defined between the plates. The gaseousfuel (either propane or natural gas) is provided by way of a pipe 67which is located just above the burner plates 50, 52 and which isconnected by a tee connection to a vertical conduit 68 having openingsin its lower end to supply the gaseous fuel centrally of the burnerplates 50, 52 in such a way as to provide a generally uniform supply tothem. As shown in the drawings (FIGS. 3, 4, 6), this centrally connectedconduit 68 has a lower end portion disposed between the burner plates(50, 52) which is provided with a multiplicity of radially arrangedopenings 70 to provide even distribution of gaseous fuel to the chamber60 between the plates 50, 52. During operation, combustion air movingalong the path of combustion air travel from the burner blower 44 entersthrough the aligned openings 62, 64 in the burner plates and mixes withthe gaseous fuel emerging from between the burner plates via theabove-mentioned annular openings 66 thereby to provide a combustiblefuel-air mixture downstream of the burner plates.

The above-mentioned openings 62, 64 in the burner plates 50, 52 are inthe form of short tubular collars 74, 76 projecting from the plates withthe tubular collars of both plates being aligned with and directedtoward each other in confronting spaced apart relation to provide theabove-noted annular openings 66 allowing exit of gaseous fuel betweenthe confronting spaced apart collars. In greater detail, the firstburner plate 50 is located upstream of the second burner plate 52relative to the flow direction of combustion air, when in use, and it isimportant to note that the tubular collars 74 of this first burner plate50 define flow passages which are smaller in diameter than those definedby the tubular collars 76 of the second plate 52. Hence, by virtue oftheir relationship as shown in the drawings and described above, thereis created a venturi-like flow action as the combustion air passesthrough the aligned tubular collars 74, 76 of the two burner plates 50,52 thus promoting thorough mixing of the air and the gaseous fuel beingsupplied by the annular openings noted above and illustrated in FIG. 6as well as allowing for reduced gas supply pressure between the burnerplates as the venturi action pulls the gas into the moving combustionair streams.

The short tubular collars 74, 76 in the burner plates 50, 52 areintegrally formed with their respective burner plates as by a punchingaction which need not be described in further detail. Alternatively theburner plates may be made by a suitable casting process.

The diameter of the first or upper burner plate 50 is slightly largerthan that of the lower plate 52. The peripheral edges of both plates areformed or turned inwardly toward each other with an annular gap 80between them. Some gas is allowed to leave the burner head through thisannular gap 80 which then mixes with air flowing around the edge of theburner head.

It is noted that the positioning of the burner blower 44 in the mannerdescribed above in relation to the burner head provides the benefits ofensuring a balanced air flow all around and through the burner headplates 50, 52. This is in contrast to traditional power burners whichrequire a very much longer distance between the burner blower and theburner head to ensure a balanced flow. The above-noted enclosures whichdefine a path of movement of combustion air from the blower areassociated with the flow straightener vanes 48 noted above to provide asmooth and uniform flow of air to the burner head.

A conventional spark igniter part of which is shown as item 81 isattached to the lower burner plate 52 and is used to light the burner ina conventional fashion. During operation, the flames extend downwardlyfrom the burner head into the interior of the combustion chamber 26. Thebottom of the combustion chamber 26 is, of course, closed forcing theflames to turn back with the hot combustion gases then made to flowaround an elongated metal shield 82 (FIG. 2) which is spaced areasonable distance away from the above-mentioned series of slot-likeopenings in the wall of the combustion chamber 26, which openings leadinto the heat exchanger sections 30 which will be described hereinafter.It is also noted that although the combustion chamber is shown in thedrawings as being of hexagonal outline as seen in plan view, it is quitepossible that other shapes, such as a circular shape, might be choseninstead.

The heat exchanger 28 comprises a stack of metal exchanger sections 30which extend away from the combustion chamber 26 and toward the exhauststack 32 in vertically spaced apart generally horizontal planes (FIGS. 7and 8). Each heat exchanger section is made from two metal panels 86,preferably of stainless steel to resist corrosion, each metal panel 86containing a series of parallel V-shaped corrugations 88 which aredisposed at an angle α to a line normal to the longitudinal axis of theheat exchanger section 30. In the particular unit noted previously, thisangle is in the order of 9° although this angle can be variedconsiderably (e.g., as for different BTU ratings). These metal panels 86are attached together in face-to-face relationship such that the peaksof the corrugations are touching or nearly touching (FIG. 10). Becausethese panels are in close proximity, as the hot combustion gases flowthrough each of the exchanger sections 30 between the metal panels 86,these gases are forced to flow into the V-shaped channels defined by thecorrugations in the panels. It is important to note that the panels 86are arranged so that the angles of the corrugations 88 therein areoriented so as to be in opposing relationship as between the two panelsof each heat exchanger section 30. In other words, adjacent corrugations88 are in a “criss-cross” relationship to each other (FIG. 14). Thus, ifthe corrugations are at an angle of about 9° to a line normal to thelongitudinal axis of the exchanger section 30, adjacent corrugations 88will be at an angle of twice this amount, e.g. at about 18° relative toeach other, keeping in mind as noted above that these 9° and 18° anglescan easily be varied considerably by several degrees. As a result ofthis relationship, the gases moving through the heat exchanger sectionsfrom the combustion chamber 26 to the exhaust stack 32 will be forced tomove in a tortuous spiraling path. For example, heated gases entering anupper channel will shift, e.g. towards the right, while gases enteringthe lower channel will shift toward the left. Eventually the gases in anupper channel will be forced to move to a lower channel and vice versa.Therefore, as these gases move through the heat exchanger sections 30,the gases are shifted right, down, left, and up in a repeating fashionthus taking the form of a series of rough spirals while moving alongthrough the heat exchanger sections. This “spiraling” action of thegases allows for an efficient transfer of heat from the combustion gasesto the metal panels 86. The combustion gases then leave the heatexchanger sections 30 and enter through the slot like openings in theexhaust stack 32 and are vented outwardly in any desired manner. Theedge portions of the heat exchanger sections 30 are of course sealed toprevent escape of combustion gases and intermixing of same with the airas it is being heated.

The blower assembly 34 for the air to be heated, as mentioned above, ispositioned within the main housing 22 on the opposite side of thecombustion chamber 26 as the heat exchanger. Cold air is drawn into thepreviously mentioned cold air inlet 38 in the end wall of the mainhousing and is sucked into the blower wheels and then expelled from theblower into the main housing interior such that the air first travelsaround the outside of the combustion chamber 26 (FIG. 2) thus receivinga certain amount of heat therefrom, following which this air then entersthe horizontal spaces between the vertically spaced apart heat exchangersections 30. Thus, this cold air picks up heat from the walls of thecombustion chamber 26 as well as the panels 86 of the heat exchangersections. As the air is flowing longitudinally between the heatexchanger sections 30, the angled corrugations 88 of a heat exchangersection above the air stream force the air in one direction while thecorrugations in the section below force it in the opposite directionthus creating a substantial amount of turbulence in the air being heatedas it travels lengthwise between the heat exchanger sections 30 thusfurther improving the efficiency of the heat transfer process. Theheated air then exits the heat exchanger 28 and travels outwardly of themain housing 22 by way of the previously mentioned hot air outlet 40 inthe exit end of the main housing. It will be obvious that the entrancesand exits from the heat exchanger are designed and well sealed toprevent any mixing of combustion gases with the air being heated.

The blower assembly 34 position described above could be changed suchthat the air travels first through the heat exchanger and then aroundthe combustion chamber. This could provide a more efficient heater butcondensation in the exhaust gases is a likely result which would have tobe dealt with, which is a reason the preferred configuration describedin detail above was adopted.

The previously noted box-like main heater housing 22 includes doublewalls 89 adjacent to the heat exchanger section (see FIG. 2) forming airchambers between these walls. Louvered openings in the bottom portionsof the outer wall panels allow ambient air to enter these chambers.Openings 90 are provided in the top of the housing wall which arepositioned near the inlet for the burner blower, it being noted that theburner assembly is itself surrounded by a rectangular box 92. Hence,during operation, the air moves upwardly between the double walls 89 ofthe main housing 22 thus ensuring that the outer walls remain coolenough as to not pose a hazard to any person making contact with it.Additionally, the upwardly rising warm air allows for some preheating ofthe inlet air to the burner assembly thus further increasing systemefficiency.

A preferred embodiment of the invention has been described by way ofexample. Those skilled in the art will realize that variousmodifications and changes may be made while remaining within the spiritand scope of the invention. Hence the invention is not to be limited tothe embodiment as described but, rather, the invention encompasses thefull range of equivalencies as defined by the appended claims.

1. A heat exchanger section comprising a pair of metal panels disposedin close face-to-face relation to allow gases to flow therebetween froman inlet end to an outlet end in a travel direction said panels eachhaving undulations or corrugations therein whereby gases flowing betweensaid panels in the travel direction are forced to move in a turbulentfashion to enhance transfer of heat between said panels and the flowinggases.
 2. A heat exchanger section comprising a pair of metal panelsdisposed in close face-to-face relation to allow gases to flowtherebetween from an inlet end to an outlet end in a travel direction,said panels each having corrugations therein angled relative to thetravel direction and oppositely oriented with respect to each other suchthat adjacent corrugations are in a criss-cross relation to each otherwhereby gases flowing between said panels are forced by the opposingcorrugations to move in the form of a series of repeating spirals fromsaid inlet end to said outlet end.
 3. The heat exchanger section ofclaim 2 wherein said corrugations are of a generally V-shaped or zig-zagconfiguration when seen end-on.
 4. The heat exchanger section of claim 2wherein said corrugations are disposed at a relatively shallow acuteangle relative to a line normal to the travel direction.
 5. The heatexchanger of claim 4 wherein said acute angle is approximately 9 degreeswith said adjacent corrugations being at an angle of approximately 18degrees relative to each other.